The use of a plastic housing for batteries is disclosed, for example in U.S. Pat. No. 4,719,159. Plastic housing for batteries affords several advantages over solid metal housings. Thermoplastic materials are relatively inexpensive. Secondly, plastic can be easily formed into complex shapes for battery housings by extrusion, injection molding, thermoforming or other processes. It is readily bonded to other plastic components to form a leak-proof seal. Also, plastic containers will rupture at relatively low internal pressures, a desirable battery safety feature.
One problem of plastic battery housings is that plastic is permeable to water vapor and organic solvent vapors. The migration of water vapor into a lithium battery and electrolyte solvent out of the battery will generally adversely affect a battery's electrical performance.